Silver halide emulsions stabilized with n-(1,3,4-thiadiazol-2-yl)-dithiocarbamic acid esters

ABSTRACT

THE STABILITY OF PHOTOGRAPHIC SILVER HALIDE EMULSIONS AGAINST SPONTANEOUS FOG FORMATION IS IMPROVED BY ADDITION OF AN N-(1,3,4-THIADIAZOL-2-YL)-DITHIOCARBAMIC ACID ESTER.

United States Patent 3,764,339 SILVER HALIDE EMULSIONS STABILIZED WITH N-(1,3,4 THIADIAZOL-2-YL)-DITHIOCARBAMIC ACID ESTERS Wolfgang Himmelmann, Opladen, Anita von Kiinig and Franz Moll, Leverkusen, Dietrich Riicker, Bietigheim, and Wilhelm Saleck, Schildgen, Germany, assignors to Agfa-Gevaert Aktiengesellschaft, Leverkusen, Germany No Drawing. Filed Sept. 8, 1971, Ser. No. 178,845 Claims priority, application Germany, Sept. 9, 1970, P 44 622.4 Int. Cl. G03c J/34 US. Cl. 96-109 4 Claims ABSTRACT OF THE DISCLOSURE The stability of photographic silver halide emulsions against spontaneous fog formation is improved by addition of an N-(1,3,4-thiadiazol-2-yl)-dithiocarbamic acid ester.

This invention relates to a photographic material comprising at least one silver halide emulsion layer whose stability is improved by the addition of N-(l,3,4-thiadiazol-2-yl)-dithiocarbamic acid esters.

It is well known that photographic emulsions on storage become spontaneously developable without exposure to light. There is normally a detectable amount of the silver salt reduced during development at unexposed areas. This phenomenon is commonly called fog or chemical fog. Fog depends both upon the nature of the emulsion and the conditions of development. For a given emulsion it increases with the degree of development. It is common practice to make accelerated tests of the stability of photographic emulsions by storage at increased temperature or humidity, or both. It is desirable to have emulsions as stable as possible under the condition of high temperature, which may occur in tropical climates. Fog usually appears over the whole area of the light-sensitive layer, but when severe is quite frequently non-uniform.

It is known that certain compounds particularly heterocyclic mercapto or imino compounds have an antifoggant and stabilizing effect when incorporated into photographic silver halide emulsions and so improve greatly the keeping qualities of the emulsions. Mostly the socalled fog-inhibitors or stabilizers form difiicultly soluble or insoblue silver compounds with the silver ions of the photographic emulsion. It is also known that inorganic or organic mercury compounds can be used as stabilizers. Many of these stabilisers however, are of liimted utility since they have a desensitizing effect or alter'the gradation.

It is among the objects of the invention to provide stabilizers which cause no reduction in the sensitivity at concentrations at which they achieve suflicient stabilization. Another object is to provide a photographic silver halide emulsion that is stable against the production of fog upon storage and stable with respect to the speed and contrast of the emulsion. Other objects and advantages 3,764,339 Patented Oct. 9, 1973 in which R represents 1) hydrogen,

(2) a saturated or olefinically unsaturated linear, branched or cyclic aliphatic group having 1 to 18, preferably 1 to 8, carbon atoms, which can be substituted by one or more halogen atoms, such as fluorine, chlorine or bromine; by alkoxy or alkylthio with preferably up to 5 carbon atoms; or by aryloxy or arylthio, preferably phenoxy or phenylthio,

( 3) alkoxy with preferably up to 5 carbon atoms,

(4) alkylthio with preferably up to 5 carbon atoms,

(5) aryl, especially a group of the phenyl series,

(6) aryloxy, preferably phenoxy,

(7) arylthio, preferably phenylthio,

(8) nitro, or

(9) alkoxyalkoxy the aryl radicals can contain further substituents, for example one or more halogen atoms and 1 to 3 alkyl groups or 1 to 3 alkoxy groups;

R stands for hydrogen or an alkyl, alkenyl or alkinyl radical of up to 4 carbon atoms preferably alkyl of up to 3 carbon atoms; and

R represents (1) a saturated or unsaturated linear, branched or cyclic aliphatic group, with preferably 1 to 8 carbon atoms, which can be substituted, for example by halogen such as fluorine, chlorine or bromine; by alkoxy or alkylthio with preferably up to 5 carbon atoms; or by aryloxy or arylthio, preferably phenoxy or phenylthio,

(2) aryl, such as a group of the phenyl or naphthyl series, or

(3) aralkyl, such as benzyl or phenylethyl whose aryl rings can be substituted with one or more alkoxy groups, alkyl groups, or halogen, for example fluorine, chlorine or bromine, the alkyl and alkoxy groups containing 1 to 3 carbon atoms.

The compounds set out-in the following tables, for examples, can be used.

TABLE 1 Compound R1 R2 R3 1 CF: H CHz'-CH=CH2 173 2 CF; H -CHa-C=CH 171 3 CF; H CH2CECH 4 CF: H 202 TABLE 1-Continued M.P., Compound R1 R2 R C.

CH: CHa 95 CH3 CHzC H=CH2 48 OH3 Cl CH CHz-CH=CH2 63 .0--- H CH 110 9 C a oH,--o1

10 [PC3131 C2115 CH: 87

11 n-CaH1 CzHs 56 -CH2- C1 12 CH(OH3): H CHzCH=CHa 108 13 CH(CH3)I CH1 CH3 44 OH2 Cl 15 CF; H CH3 I 218 16 OF H 224 Q 17- OH -O- H CH; 111

18.. CH O-(CH2)zO- H CH; 69

(CHa)2CHS- H CH; 61

.......... CH CH--S H 167 21- C -O- CH O OH H 168 z 2):- 2)2- OHr Q61 22.. CHa-O(CH2)z-O(CH2)r- H --CH:CH=CH1 72 C H 0CH H 232 23 5- 2. "'CHPQCI Cl 0-9112- ---CH C! 25.. H CH: 173

C1 S-CH2 C1- S-CH-r- -OH2- C1 (31- S-CHr- -CH 28 CH: CH: 183

The aforementioned compounds are prepared in subin which stantial accordance with known methods by reacting 2- amino-1,3,4-thiadiazoles corresponding to the formula:

in whichrrRl and R are as defined above,

with carbon disulfide in the presence of a diluent and a base to form a salt of dithiocarbamic acid corresponding to the formula:

I I B m s E (III) R and R are again as defined above, whilst Me represents an alkali metal atom or a quaternary ammonium group.

This intermediate product is then alkylated with an alkyl or aryl halide of the general formula:

dimethyl sulfoxide, alcohols, water, ethers such as tetrahydrofuran and dioxan. Any of the usual acid-binding agents, such as alkali metal hydroxides, alkali metal carbamates, alkali metal alcoholates or tertiary amines, can be used as the bases.

The reaction temperatures can be varied within a relatively wide range, although in most instances the reaction is carried out at a temperature of from C. to 100 C. To prepare the compounds, it is best to mix equimolar quantities of the Z-amino-l,3,4-thiadiazole, carbon disulfide and alkali metal hydroxide at a temperature from 0 to C., followed by addition of an equivalent quantity of an alkylating agent after 30 minutes. After the exothermic reaction has abated, the reaction product is worked up in the usual way.

PREPARATION OF COMPOUND 15 A solution of 17 g. (0.3 mol) of potassium hydroxide in 100 ml. of water is added to a solution of 50.7 g. (0.3 mol) of 2-amino-5-trifluoromethyl-1,3,4-thiadiazole in 300 ml. of dimethyl formamide. This is followed by the addition of 22.8 g. (0.3 mol) of carbon disulfide, after which the reaction mixture is stirred for 1 hour, and then 37.8 g. (0.3 mol) of dimethyl sulfate are added dropwise. Following dilution with water, the deposit formed is suction filtered and recrystallised from ethanol. The resulting N-(S-trifluoromethyl-l,3,4-thiadiazol-2-yl)- dithiocarbamic acid methyl ester melts at 218 C.

PREPARATION OF COMPOUND 16 A solution of 6.8 g. (0.12 mol) of potassium hydroxide in 40 ml. of water is added to a solution of 20.3 g. (0.12 mol) of 2-amino-5-tridiuoromethyl-1,3,4-thiadiazole in 200 ml. of dimethyl formamide. Following the addition of 9.2 g. (0.12 mol) of carbon disulfide, the reaction mixture is stirred for 1 hour. 15.2 g. (0.12 mol) of benzyl chloride are then added dropwise, after which the mixture is heated for 2 hours at 60 C. and is then poured on to ice/water. The precipitate is suction filtered and recrystallised from ethanol. The resulting N-(S-trifluoromethyl-1,3,4-thiadiazol-2-yl)-dithiocarbamic acid benzyl ester melts at 224 C The N-(1,3,4-thiadiazol-2-yl)-dithiocarbamic acid esters used in accordance with the invention have the advantage over a number of conventional stabilizers in that they do not contain any free mercapto groups. The photographic properties such as sensitivity, gradation and clarity are excellently stabilised by the compounds used according to the invention and they cause no fogging or adverse effect upon grain.

As mentioned above, many prior stabilizers that are particularly effective in preventing fogging cause reduction in the sensitivity of the freshly produced photographic material. Other prior stabilizers which sufliciently inhibit fog formation (cause a more or less pronounced, but in any event undesirable, change in sensitivity, usually accompanied by flattening of the gradation during storage. By contrast, the N-(1,3,4-thiadia-zol-2-yl)-dithiocarbamic acid esters used according to the present invention effectively prevent fog formation without deleteriously effecting gradation and sensitivity.

The N-(1,3,4-thiadiazol-2-y1)-dithiocarbamic acid esters used according to the present invention can be added either to silver halide layers or to other water-permeable layers for example to intermediate layers, protective layers or to the baryta-coatings which contact the silver halide layers. When these compounds are added to lightsensitive silver halide emulsions, this can be done at any stage during preparation of the emulsion. They are preferably added before after-ripening. The quantity added can be varied within wide limits. Quantities of from 0.001 to 5 g. per mol of silver halide have generally proved to be adequate. Particularly good results are obtained when the emulsion contains 1 to 50 mg. of the stabilizer per mol of silver halide.

It is advantageous to add the stabilizer in the form of a solution. Examples of suitable solvents include lower alcohols, such as methanol, ethanol or propanol, tetrahydrofuran, acetone and dimethyl formamide.

The usual silver halide emulsions are suitable for the present invention. The silver halide may be silver chloride, silver bromide or a mixture thereof, which may additionally contain a small amount of silver iodide of up to 10 mol percent.

Gelatin is preferably used as binder for the photographic layer. It can, however, be replaced, either wholly or in part, by other natural or synthetic binders. Examples of suitable natural binders include alginic acid and its derivatives, such as its salts, esters, or amides; cellulose derivatives such as carboxymethyl cellulose and alkyl celluloses such as hydroxyethyl cellulose; starch or its derivatives such as its ethers or esters; and carrageenates. Polyvinyl alcohol, partially hydrolysed vinyl acetate, polyvinyl pyrrolidone and the like are examples of suitable synthetic binders.

The emulsions can also be chemically sensitized, for example by the addition during chemical ripening of sulphur-containing compounds, for example allyl isothiocyanate, allyl thiourea, and sodium thiosulfate. Reducing agents can also be used as chemical sensitisers, for example the tin compounds described in Belgian patent specification No. 493,464 or 568,687, polyamines such as diethylene triamine, or aminomethyl sulphinic acid derivatives, for example those of the kind described in Belgian patent specification No. 547,323.

Other suitable chemical sensitisers include noble metals or compounds of noble metals, such as gold, platinum, palladium, iridium, ruthenium or rhodium. This method of chemical sensitisation is described in the article by R. Koslowsky in Z. Wiss. Phot. 46, 65-72 (1951).

It is also possible to sensitise the emulsion with polyalkylene oxide derivatives, for example with polyethylene oxide having a molecular weight of from 1000 to 20,000, and also with condensation products of alkylene oxides and aliphatic alcohols, glycols, cyclic dehydration products of hexitols, with alkyl-substituted phenols, aliphatic carboxylic acids, aliphatic amines, aliphatic diamines and amides. The condensation products have molecular weights of at least 700, and preferably of more than 1000. In order to produce special effects, these sensitisers can of course be used in combination with one another, as described in Belgian patent specification No. 537,278 and in British patent specification No. 727,982.

The emulsions can also be optically sensitized, for example with the conventional polymethine dyes such as neutrocyanines, basic or acid carbocyanines, thiocyanines, hemicyanines, styryl dyes, or oxonols. Sensitisers of this kind are described in the work by F. M. Hamer The Cyanine Dyes and Related Compounds (1964).

In addition to the N-(1,3,4-thiadiazol-2-yl)-dithiocarbamic acid esters, the emulsions can contain known stabilisers, for example homopolar or saltlike compounds of mercury with groups containing aromatic or heterocyclic rings, such as mercapto triazoles, simple mercury salts, sulphonium mercury double salts, and other mercury compounds. Other suitable stabilisers include azaindenes, preferably tetraor penta-azaindenes, especially those substituted by hydroxy or amino groups. Compounds of this kind are described in the article by Birr in Z. Wiss. Phot., 47, 2-58 (1952). Other suitable stabilisers include inter alia heterocyclic mercapto compounds, for example phenyl mercapto tetrazole, quaternary benzthiazole derivatives, or benzotriazole.

The emulsions can be hardened in the usual way, for example with formaldehyde or halogen-substituted aldehydes containing a carboxyl group, such as mucobromic acid, diketones, methane sulphonic acid esters, and dialdehydes.

The emulsions can also contain colour couplers in dissolved or dispersed form.

The stabilizers which we have described may be used in various kinds of photographic emulsions. In addition to being useful in X-ray and other non-optically sensitized emulsions they may also be used in ortho-chromatic, panchromatic and infrared-sensitive emulsions. They may also be used for emulsions suitable for use in the silver salt diffusion process for color-photography and for photographic materials for the silver dye bleach process.

EXAMPLE 1 A highly sensitive silver bromide/iodide emulsion containing 6 mol percent of silver iodide is prepared in the usual way, the silver nitrate solution being run at intervals into a solution containing gelatin, potassium bromide and potassium iodide. The emulsion is then flocculated in known manner with ammonium sulfate and freed from the usual salts. The flocculate is redispersed in warm water, and the required quantity of sulfur-containing ripening gelatin is added, followed by ripening in the presence of gold (I) thiocyanate complexes and sodium thiosulfate up to optimum sensitivity.

Before the emulsion is heated to the ripening temperature, it is divided into 22 portions. The first portion is ripened in the absence of any other additives, whilst the compounds mentioned in the following Table 2 are individually added to the other portions.

8 Sodium citrate Potassium bromide Made up with water to 1 litre.

. EXAMPLE 2 A highly sensitive silver bromide/iodide emulsion containing 5 mol percent of silver iodide is prepared in the usual way, silver nitrate solution being run into a solution containing gelatin,potassium iodide and potassium bromide. The emulsion is flocculated in known manner with ammonium sulfate and freed from soluble salts by washing. The flocculate is redispersed in warm water, and the required quantity of sulfur-containing ripening gelatin is added, followed by ripening to optimum sensitivity in the presence of gold (I) -thiocyanate complexes and sodium thiosulfate. V

200 mg. of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene as stabiliser, 600 mg. of saponin as wetting agent, and 10 ml. of a 10% by weight aqueous solution of formalde- TABLE 2 3 days storage in a heating cupboard, 7 minutes develop- Mg. per 7 minutes development time 16 minutes development time ment time Compound moi number Ag X S 'y Fog S 'y Fog S y Fog Standard 1. 15 0. 16 Standard 1. 30 0. 24 1. 0.90 0. 35

s. 0 +1. 0 0. 95 o. 119 +0. 5 1. 2s 0. 22 -1.s Y o. to 0. 2.5

5. 0 :bll 1. 10 0. 13 =|=0 1. 20 0. 17 1. 0 1. 00 0. 22

N own-S =sensitivity; 3 DIN=1 shutter stop.

position:

G. Sodium sulfite sicc. 70.0 Borax 7.0 Hydroquinone 3.5 p-Monomethylaminophenol sulfate 3.5

hyde, based in each instance on 1 kg. of emulsion, are then added to the emulsions. The emulsion is then divided into 19 portions. One portion is left without any additives, whilst the other portions contain the compounds mentioned in the table below. 7

The emulsions are cast on to a support of cellulose acetate, and are dried and then exposed and developed as already described. Some of the samples are stored for 3 days at60 C. and then developed for 16 minutes at 20 C.

The results of sensitometric testing are set out in the following table. It is apparent from this tablet that a distinct fog-stabilising effect is noticeable, even in a heating cupboard. Accordingly, the substances can be added TABLE 3 3 days storage in a heating cupboard, 16 minutes develop- Mg. per 7 minutes development time 16 minutes development time ment time Compound mol of number Ag X S 'y Fog S 'y Fog S 'y Fog Standard 1. O. 15 Standard 1. 20 0. 22 0. 1. 05 O. 35 3 0. 5 1. 07 0. =i:0 1. 20 0. =1=0 1. 22 0. 3 -0. 5 1. 00 0. 10 +0 1. 0. 16 510 1. 10 0. 23 3 :l=0 1. 05 0. 10 0. 5 1. 20 0. 14 =i=0 1. 15 0. 19 3 -0. 5 1. 00 0. 09 -0. 5 1. 20 0. l4 =1=0 1. 15 0. 19 3 =4;0 1. 00 0. 08 +0 1. 25 0. 12 :i;0 1. 20 0. 17 15 0. 5 1.00 0. 12 1. 0 1.15 0. 17 :b0 1. 05 0.22 3 -0. 5 1. 05 0. 12 0. 5 1. 25 0. 18 :l:0 1. 20 0. 23 15 510 1.05 0.10 -0. 5 1.10 0.13 0. 5 1.10 0.18 3 +0. 5 1. 06 0. 13 :ED 1. 26 0. 19 i0 1. 10 0.25 3 +0. 5 1. 1O 0. 12 510 1. 25 0. 18 i0 1. 15 0.23 3 i0 1. 00 0. 11 =|=0 1. 2O 0. 18 510 1. 0. 22 3 1 5 0.95 0. 10 1. 5 1. 05 0. 12 -1. 0 1. 00 0.19 3 i0 1.05 0. l2 -0. 5 1. 25 0. 18 +0. 5 1. 30 0. 20 15 510 1. 15 0. 11 =b0 1. 25 0. 15 +0. 5 1. 25 0. 20 3 0. 5 1. 00 0. 10 0. 5 1. 20 0. 17 =l=0 1. O5 0. 24 15 =b0 1.05 0. 10 0. 5 1. 10 0. 13 -0. 5 1. 10 0. 13 15 :l:0 1. 00 0. 11 0. 5 1. l5 0. 16 0. 5 1. 20 0. 28 3 i0 1. 00 0. 10 0. 5 1. 20 0. 16 =i=0 1. 15 O. 20

No'rE.-S=sensitivity; 3 DIN=1 shutter stop.

What is claimed is:

1. A light-sensitive photographic silver halide emulsion which contains in an amount that inhibits fogging, an N-(1,3,4-thiadiazol-2-yl)-dithiocarbamic acid ester of the formula:

l R1 NC-SR3 s n S in which 2. The photographic material of claim 1, wherein R represents hydrogen or an alkyl radical having 1 to 3 carbon atoms.

3. The photographic material of claim 1, wherein R represents trifiuoromethyl or alkylthio with up to 5 carbon atoms.

4. The photographic material of claim 1 wherein R represents methyl or chlorobenzyl.

References Cited UNITED STATES PATENTS 3,598,598 8/1971 Herz 96109 3,640,719 2/1972 Konig et a1. 96-109 FOREIGN PATENTS 220,166 3/1962 Austria 96-109 NORMAN G. TORCHIN, Primary Examiner W. H. LOUIE, IR., Assistant Examiner 

